Smoke and mirrors.
No, it works for anything. Any program ever. Not just gcc. Anything that takes the classic "inputs --> program --> outputs" approach should work fine.
Win2K/XP. Might work on others, I'm not sure. You probably need debugging privileges as well, but you probably already have them if you're compiling programs.
No, I've left that as an exercise to the reader. If anyone's up for the task, I'd love to hear from them.